The present invention relates to an implosion-protected cathode-ray tube comprising a bulb, and a metallic band tight binding a front outer peripheral portion of the bulb near the front face of the bulb, and designed for efficient mass production.
Because it is evacuated to a high vacuum and continuously subjected to a pressure corresponding to the atmospheric pressure, the cathode-ray tube can implode suddenly if the surface of the glass bulb is damaged or an impact is applied thereto resulting in a dangerous scattering of pieces of broken glass. Various means have been proposed and applied to the cathode-ray tube to prevent the implosion of the cathode-ray tube. A currently most prevalent means for avoiding the implosion of the cathode-ray tube and the resulting scattering of pieces of broken glass even when the airtightness of the bulb is broken employs a metallic band tightened around a largest outer peripheral portion of the bulb near the front face to bind the largest front portion tight so that stress induced in the bulb by the atmospheric pressure is relaxed and the propagation of cracks may be suppressed.
In most cases, the metallic band is tightened around the largest outer peripheral portion of the bulb after the heating and evacuation of the cathode-ray tube to prevent implosion. A stress is induced in the evacuated glass bulb by the pressure difference between the outside and inside of the glass bulb and by the sudden drop of the temperature of the glass bulb when the glass bulb is taken out after the heating and evacuation from a heating furnace heated at a temperature on the order of 400.degree. C. Accordingly, there is a danger that the bulb can implode suddenly and pieces of broken glass can scatter in the heating and evacuation process including the process of taking out the bulb from the heating furnace, when the bulb has cracks or an impact is applied to the bulb. Recently, such a danger has progressively increased with the increasing use of large cathode-ray tubes having a nearly flat face. As stated in Japanese Patent Laid-Open No. 62-5533, even if a metallic band is tightened around the largest outer peripheral portion of a bulb prior to the heating and evacuation process, the metallic band provides a thermal expansion greater than that of the glass bulb in the heating furnace during the heating and evacuation process when any special consideration is not given, so that the metallic band is unable to exert its effect properly.